A local area network (LAN) may include a computer network covering a small physical area that may connect electronic devices, such as computers, printers, switches, routers, telephones, firewalls, or other electronic devices. A LAN may communicate using Ethernet technology and may provide high data transfer rates, the ability to share peripheral devices, increased security, and sharing of data and applications from a central location. A customer may operate two or more LANs on different customer sites that are physically remote and may desire to combine the customer sites into a single network. A network service provider may provide a virtual private LAN service (VPLS) over a network (e.g., the Internet), which may emulate a point-to-point LAN connection over the network, allowing the physically remote LANs to behave as if part of a single Ethernet domain.
In VPLS environments, there may be instances when a single customer site is multi-homed (e.g., dual-homed) to two or more provider edge (PE) devices that are on/connected to a VPLS core (network) in order to provide redundant connectivity. A PE device may include any network element with routing functions (e.g., a router). Each one of the PE devices may be connected to a corresponding customer edge (CE) device on/connected to a customer site (e.g., a LAN). A CE device may include a switch or a router that acts as a gateway from the customer site to the VPLS (service provider's network).
One PE device may act as a primary PE device for connecting the customer site to the VPLS core, and the other PE device may serve as a backup PE device. The primary PE device and the backup PE device may participate in a spanning tree protocol (STP) to create only one spanning tree (ST) for the customer site. The primary PE device may act as a root bridge to create a connection between the primary PE device and the corresponding CE device, connecting the customer site to the core VPLS (by the primary PE device forwarding data/packets it receives). The backup PE device may block its port connecting it to its corresponding CE device in order to block a redundant connection between the customer site and the core VPLS.
When a break (e.g., connection failure) occurs on the customer site, the customer site may split into two separate sites/networks (e.g., site 1a and site 1b). Site 1a may be connected to the core VPLS through the original primary PE device and the corresponding CE device located on/connected to site 1a. Once the break occurs, an STP on site 1b may cause the original backup PE device to unblock (i.e., also become a root bridge) to connect site 1b to the core VPLS through the original backup PE device and the corresponding CE device located on site 1b. The unblocking (e.g., topology change event) may prompt the original PE device to send out message(s) (e.g., Topology Change Notification (TCN) message(s)) to flush all of the media access control (MAC) tables on site 1b. MAC tables may identify routes to destination device(s) (e.g., end hosts (devices) on/connected to site 1a). Flushing allows devices to relearn all the MAC addresses and the corresponding proper routes to other devices.
However, since the original primary PE device may continue to operate normally (e.g., no topology event is observed), the original primary PE may not send out a message to flush all the MAC tables on site 1a. As a result, devices on site 1a will not be able to send packets/data to devices on site 1b. The devices on site 1a may initially send out packets via routes based on information that existed before the break, and the data/packets will be dropped. The devices on site 1a may keep resending the packets based on the wrong routes until the devices receive traffic from site 1b or MAC aging occurs. MAC aging may occur when a MAC address is not used during a predefined period of time. The MAC table may flush out the corresponding information after the predefined period of time. In both cases, resources (used by resending the packet) and time may be wasted.
An STP (PWs) may be run, not only over the original customer site, but also over the VPLS core and other customer sites connected to the VPLS core to prompt MAC flushes at all sites. As a result, the original customer site, the VPLS core, and the other sites may become one big ST. This may create scaling issues, prompt unnecessary flushes of other customer sites, slow down the sites and the VPLS, and exert more resources. Furthermore, in many cases, STs may be run locally on each site and extending the ST may not be possible.